Extensions was released on October 31, 1979 and debuted on Billboard’s Top Pop Album charts on December 8, 1979.

Extensions began what Alan recalls as « a new chapter for the group. » Artistically and commercially, their fourth studio album was one of several new levels: It was the first one with Cheryl Bentyne, who had replaced Laurel Masse. Cheryl proved to be the perfect complement to the group’s already dynamic style and performance. It was also the first album that contained hits in both the jazz and pop categories. « Twilight Zone/Twilight Tone » went to #30 and « Trickle, Trickle » went to #73 on the Billboard’s Hot 100 chart. Overall, the album peaked at #55 on the Billboard Top LP’s chart. « A very exciting time, » Janis remembers.

The most widely known song from the album, « Birdland, » is the cut that earned the group its first Grammy Award. (Best Jazz/Fusion Performance, Vocal or Instrumental) Janis received a Grammy for her vocal arrangement of « Birdland » as well. « Birdland » was the most played jazz record of 1980. Many regard that particular tune as the signature song of The Manhattan Transfer. A remake of the Weather Report song, it had new lyrics written for the group by Jon Hendricks. Originally, Eddie Jefferson was writing the new lyrics, but he was killed before finishing them. The album is dedicated to him.

Jay Graydon produced Extensions. « It was great working with him, » Alan adds. Janis also recalls that they worked at Jay’s house « till wee hours. » She also recalls that it was so hot at Jay’s house that Claire Fischer conducted « A Foreign Affair » with his shirt off! Alan’s songwriting talent also surfaced on this release, as he wrote « Twilight Zone/Twilight Tone » with Graydon. Visually, the group wore futuristic costumes designed by Jean-Paul Gaultier that gave them a distinctive look onstage (as well as on the back of the album cover.) The audiences loved it, and the album tour was widely successful at home and especially in Europe. All of the hard work paid off, as Extensions is a landmark album for the group.